Obtain only first 6 characters in a column of all rows in the table?

If I only want to use first 6 characters in one column A to match the other column B with only 6 characters, can I still use RTRIM? However, I know the RTRIM is single row function. Hence, I am not sure whether I could run the following? Or do you have a correct way to implement this selection?

Table prod: columnA varchar2(10)
Table sale: colunmB varchar2(6)

select RTRIM( columnA, 4) from prod where RTRIM( columnA, 4) in (select columnB from sale);

Thanks.
Maggie Received on Wed Jul 19 2000 - 00:00:00 CDT